A new method, termed autoprogressive training, for training neural networks to learn complex stress-strain behaviour of materials using global load-deflection response measured in a structural test is described. The richness of the constitutive information that is generally implicitly contained in the results of structural tests may in many cases make it possible to train a neural network material model from only a small number of such tests, thus overcoming one of the perceived limitations of a neural network approach to modelling of material behaviour; namely, that a voluminous amount of material test data is required. The method uses the partially-trained neural network in a central way in an iterative non-linear finite element analysis of the test specimen in order to extract approximate, but gradually improving, stress-strain information with which to train the neural network.An example is presented in which a simple neural network constitutive model of a T300/976 graphite/ epoxy unidirectional lamina is trained, using the load-deflection response recorded during a destructive compressive test of a [($45) ] 1 laminated structural plate containing an open hole. The results of a subsequent forward analysis are also presented, in which the trained material model is used to simulate the response of a compressively loaded [($30) ] 1 structural laminate containing an open hole. Avenues for further improvement of the neural network model are also suggested.The proposed autoprogressive algorithm appears to have wide application in the general area of Non-Destructive Evaluation (NDE) and damage detection. Most NDE experiments can be viewed as structural tests and the proposed methodology can be used to determine certain damage indices, similar to the way in which constitutive models are determined.
While aortic valve root compliance and leaflet coaptation have significant influence on valve closure, their implications have not yet been fully evaluated. The present study developed a full fluid-structure interaction (FSI) model that is able to cope with arbitrary coaptation between the leaflets of the aortic valve during the closing phase. Two simplifications were also evaluated for the simulation of the closing phase only. One employs an FSI model with a rigid root and the other uses a "dry" (without flow) model. Numerical tests were performed to verify the model. New metrics were defined to process the results in terms of leaflet coaptation area and contact pressure. The axial displacement of the leaflets, closure time and coaptation parameters were similar in the two FSI models, whereas the dry model, with imposed uniform load on the leaflets, produced larger coaptation area and contact pressure, larger axial displacement and faster closure time compared with the FSI model. The differences were up to 30% in the coaptation area, 55% in the contact pressure and 170% in the closure time. Consequently, an FSI model should be used to accurately resolve the kinematics of the aortic valve and leaflet coaptation details during the end-closing stage.
SUMMARYThis study presents a numerical integration method for the non-linear viscoelastic behaviour of isotropic materials and structures. The Schapery's three-dimensional (3D) non-linear viscoelastic material model is integrated within a displacement-based ÿnite element (FE) environment. The deviatoric and volumetric responses are decoupled and the strain vector is decomposed into instantaneous and hereditary parts. The hereditary strains are updated at the end of each time increment using a recursive formulation. The constitutive equations are expressed in an incremental form for each time step, assuming a constant incremental strain rate. A new iterative procedure with predictor-corrector type steps is combined with the recursive integration method. A general polynomial form for the parameters of the non-linear Schapery model is proposed. The consistent algorithmic tangent sti ness matrix is realized and used to enhance convergence and help achieve a correct convergent state. Veriÿcations of the proposed numerical formulation are performed and compared with a previous work using experimental data for a glassy amorphous polymer PMMA.
Calcific aortic valve (AV) disease has a high prevalence in the United States, and hypertension is correlated to early onset of the disease. The cause of the disease is poorly understood, although biological and remodeling responses to mechanical forces, such as membrane tension, have been hypothesized to play a role. The mechanical behavior of the native AV has, therefore, been the focus of many recent studies. In the present study, the dynamic deformation characteristics of the AV leaflet and the effects of hypertension on leaflet deformation are quantified. Whole porcine aortic roots were trimmed and mounted in an in vitro pulsatile flow loop and subjected to normal (80/120 mmHg), hypertensive (120/160 mmHg), or severe hypertensive (150/190 mmHg) conditions. Local valve leaflet deformations were calculated with dual-camera photogrammetry method: by tracking the motion of markers placed on the AV leaflets in three dimensions and calculating their spatial deformations. The results demonstrate that, first, during diastole, high transvalvular pressure induces a stretch waveform which plateaus over the diastolic duration in both circumferential and radial directions. During systole, the leaflet stretches in the radial direction due to forward flow drag forces but compresses in the circumferential direction in a manner in agreement with Poisson's effect. Second, average diastolic and systolic stretch ratios were quantified in the radial and circumferential directions in the base and belly region of the leaflet, and diastolic stretch was found to increase with increasing pressure conditions. dynamic stretch; dynamic strain; hypertension; dual-camera photogrammetry CALCIFIC AORTIC VALVE (AV) disease has a high prevalence, especially among the elderly (16). In the Unites States alone, AV disease is the third most common cardiovascular pathology and is a strong risk factor for other cardiac-related deaths (17,18,21). Every year, nearly 95,000 procedures are performed on the AV, making AV surgeries second only to the coronary bypass procedure (13,27). The number of patients requiring AV surgery is expected to triple by 2050 (34). A calcified AV has increased thickness, collagen fiber disarray, and deposition of calcium, and thus has a drastically reduced leaflet flexibility, disabling native valve kinematics and function, resulting in AV stenosis and/or regurgitation and heart failure (19).The majority of AV calcification has an idiopathic etiology. Recent studies have shown that AV sclerosis is an active process akin to atherosclerosis, involving lipoprotein deposition, chronic inflammation, and active leaflet calcification mediated by cell differentiation (11). Furthermore, in a manner similar to the correlation between adverse hemodynamic/mechanical environment and atherosclerosis formation (9, 10), data in the literature suggest that adverse mechanical forces may elicit pathological responses of AV leaflets. Isolated mechanical forces, including stretch, pressure, and fluid shear, have been shown to affect the remod...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.